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FAQ

General​

What is Mercury?​

Mercury is a desktop API client written in Rust with egui. It's a single native binary with no Electron or web view, and it stores requests as plain .json files in a folder you choose.

Is it free?​

Yes. Mercury is MIT-licensed and open source, with no account or subscription. The source is at github.com/Harry-kp/mercury.

Which platforms are supported?​

Releases are built for macOS (Apple Silicon and Intel), Linux (x86_64 and ARM64) and Windows (x64). See Installation.

Where is my data stored?​

  • Requests and environments are in your workspace folder, as .json and .env* files.
  • App data is in ~/.mercury/: state.json (the last session), recent.json (unsaved requests you've sent) and history.json (request history). Set the MERCURY_HOME environment variable to use a different directory.

Mercury doesn't upload anything. Network requests go only to the APIs you call and, if you use the Help menu, to GitHub links opened in your browser.

Are there settings?​

No. The timeout (30 s), redirect handling and response size limits are fixed. See Defaults.

Migration​

How do I import from Postman or Insomnia?​

Use Import from Postman… or Import from Insomnia… in the workspace menu (the folder chip in the top bar). See Import & Export for what gets imported and where the files go.

How do I get requests out of Mercury?​

Request files are plain JSON, so you can copy them, commit them or send them to someone. To share one request, press ⌘ Shift C to copy it as a cURL command.

Requests​

My request doesn't send​

  • The URL needs to include http:// or https://.
  • If a message says "Request timed out after 30s", "Connection failed" or "SSL/TLS error", check the network, VPN or proxy.
  • Press Esc to cancel a request that is stuck.

My {{variable}} is sent literally​

The selected environment doesn't define it. Check the environment picker at the top right, and check that the file is in the workspace root. Only one environment is active at a time. See Environments.

How do I send form data?​

Set the header and write the body yourself:

Content-Type: application/x-www-form-urlencoded
username=john&password=secret

Can I upload files (multipart)?​

No. Multipart bodies aren't supported.

Does Mercury support GraphQL?​

You can send GraphQL as a normal POST with a JSON body and Content-Type: application/json:

{ "query": "{ users { id name } }" }

There's no schema explorer.

WebSockets, gRPC?​

Not supported. Mercury only sends HTTP requests.

Are cookies kept?​

Yes, for the current session only. See Cookies.

Troubleshooting​

Mercury won't start​

  • macOS: if Gatekeeper blocks Mercury, open System Settings → Privacy & Security and click Allow Anyway.
  • Windows: at the SmartScreen prompt, click More info, then Run anyway.

Edits from my editor don't show up​

Mercury reloads the open request when its file changes, unless you have unsaved edits in Mercury (shown by a dot after the name in the breadcrumb). In that case Mercury keeps its own version. For edits to .env values, select the environment again in the picker.

A large response isn't displayed​

Text bodies over 100 KB aren't shown inline. Click Save and open the file in an editor. Responses that declare a Content-Length over 10 MB aren't downloaded. See Performance.

Contributing​

Bug reports and pull requests are welcome on GitHub. Report an issue in the ⋯ menu opens the issue tracker. When you report a bug, include your Mercury version, your OS, the steps to reproduce, and what you expected to happen.